Top Line: Yesterday, we reviewed acute toxicity outcomes from the hypo-FLAME trial that tested an isotoxic simultaneous integrated boost to MRI-defined disease using 5-fraction SBRT.
The Study: Here we have another single center, phase 2 trial of prostate stereotactic body radiation (SBRT) with simultaneous integrated boost (SIB) in patients with low and intermediate risk disease. In this trial, patients were simulated with and without a foley to delineate the urethra and fiducial markers (56%) and rectal hydrogel spacer (51%) were used at physician discretion. They also included patients regardless of whether they could have an MRI or if the MRI showed no clinically significant lesion. The clinical target volume (CTV) consisted of the prostate and proximal seminal vesicles, and the planning target volume (PTV) was a 3-4 mm margin except 1.5-2.5 mm posterior. In the MRI-positive group (n=100), the PTV was cropped 2 mm away from the rectum, urethra, and bladder was prescribed 40 Gy in 5 fractions. The PTV overlapping these structures received 36.25 Gy, and the gross tumor volume (GTV) received up to 45 Gy. Of note, when the GTV was within 2 mm of an organ at risk, that portion of the GTV received 40 Gy. In patients who didn’t have an MRI or if there was no visible lesion on MRI (n=14), the PTV outside the rectum, urethra, and bladder received a uniform 37.5 Gy, while the PTV overlapping received 36.25 Gy. Treatment was delivered every other day. At 6 weeks after treatment, there were no grade 3 events, and the cumulative incidence of grade 2 GU and GI toxicity was 38% and 4%, respectively. There was only 1 late grade 3 event (obstruction), and the cumulative incidence of late grade 2 GU and GI toxicity at 24 months was 13% and 5%, respectively.
TBL: This phase 2 study shows that dose-escalated prostate SBRT with simultaneous integrated boost to MRI-defined disease results in relatively low acute and late toxicity when respecting OAR dose constraints. | Morris, Int J Radiat Oncol Biol Phys 2023
The Study: Here we have another single center, phase 2 trial of prostate stereotactic body radiation (SBRT) with simultaneous integrated boost (SIB) in patients with low and intermediate risk disease. In this trial, patients were simulated with and without a foley to delineate the urethra and fiducial markers (56%) and rectal hydrogel spacer (51%) were used at physician discretion. They also included patients regardless of whether they could have an MRI or if the MRI showed no clinically significant lesion. The clinical target volume (CTV) consisted of the prostate and proximal seminal vesicles, and the planning target volume (PTV) was a 3-4 mm margin except 1.5-2.5 mm posterior. In the MRI-positive group (n=100), the PTV was cropped 2 mm away from the rectum, urethra, and bladder was prescribed 40 Gy in 5 fractions. The PTV overlapping these structures received 36.25 Gy, and the gross tumor volume (GTV) received up to 45 Gy. Of note, when the GTV was within 2 mm of an organ at risk, that portion of the GTV received 40 Gy. In patients who didn’t have an MRI or if there was no visible lesion on MRI (n=14), the PTV outside the rectum, urethra, and bladder received a uniform 37.5 Gy, while the PTV overlapping received 36.25 Gy. Treatment was delivered every other day. At 6 weeks after treatment, there were no grade 3 events, and the cumulative incidence of grade 2 GU and GI toxicity was 38% and 4%, respectively. There was only 1 late grade 3 event (obstruction), and the cumulative incidence of late grade 2 GU and GI toxicity at 24 months was 13% and 5%, respectively.
TBL: This phase 2 study shows that dose-escalated prostate SBRT with simultaneous integrated boost to MRI-defined disease results in relatively low acute and late toxicity when respecting OAR dose constraints. | Morris, Int J Radiat Oncol Biol Phys 2023